In the present invention relates to a rotary throttle valve type carburetor and accelerator system for an internal combustion engine mounted on a carrying work machine, such as a temporary sweeper, and more specifically, to a rotary throttle valve type carburetor having a fuel delivery circuit that controls the amount of fuel delivered to an engine during acceleration and/or high-speed operation of the engine.
In a conventional rotary throttle valve type carburetor for an internal combustion engine as illustrated in FIG. 3, a check valve 53 and a fuel jet 7 are disposed along and mounted in a fuel passage 8a that connects a fuel supply nozzle 5 with a constant pressure fuel chamber 13. The fuel supply nozzle 5 is fixed at the bottom of a valve chamber 2 which is defined in a carburetor body 30. A rotary throttle valve 3 is movably fitted within the valve chamber 2 of the carburetor body 30. An intermediate wall 38 is connected to the bottom of the carburetor body 30, and a constant pressure fuel chamber 13 is disposed under the intermediate wall 38.
In the conventional rotary throttle valve type carburetor of FIG. 3, the length of the fuel passage 8a that connects the constant pressure fuel chamber 13 with the fuel supply nozzle 5 is short. As a result, the amount of fuel fed and delivered into the valve chamber 2 via the fuel passage 8a and the fuel supply nozzle 5 increases, in an undesirable geometric series manner, and becomes excessive as the number of revolutions per minute or speed of the engine increases. Such an excessive increase in the amount of fuel is represented by a solid curve 55 illustrated in FIG. 2. Although the amount of fuel fed from the constant pressure fuel chamber 13 is indeed adjusted by the fuel jet 7, the fed amount of fuel is still undesirably excessive upon full admission or opening of the rotary throttle valve 3.
Regarding the particular relationship between the number of revolutions per minute of the engine and the amount of fuel fed to the engine, a more desired and/or required characteristic of the relationship is that both (1) a necessary and proper amount of fuel be secured upon idling, and (2) the amount of fed fuel increases nearly linearly (such as in an arithmetic series) in proportion to the number of revolutions per minute of the engine, as represented by a dashed curve 54 illustrated in FIG. 2.
In light of the above, there is a present need in the art for a rotary throttle valve type carburetor which will enable an internal combustion engine to both (1) secure a necessary amount of fuel during low-speed operation (such as during idling) of the engine, and (2) have an improved fuel delivery characteristic during acceleration and/or high-speed operation of the engine.
The present invention provides a circuit for delivering fuel into a valve chamber defined in a carburetor body of a rotary throttle valve type carburetor for an engine. The fuel delivery circuit basically includes a fuel supply nozzle, protruding into the valve chamber and fixed at the bottom of the valve chamber to the carburetor body, and an intermediate wall. The intermediate wall is connected to the bottom of the carburetor body. The intermediate wall has a first chamber defined therein, a second chamber defined therein, and structure which cooperatively defines a first passage and a second passage therein. The first passage communicates the first chamber to the fixed end of the fuel supply nozzle, and the second passage communicates the second chamber to the first chamber. In addition, the fuel delivery circuit also basically includes an enclosure having a pressurized fuel chamber disposed under the intermediate wall, wherein the intermediate wall structure cooperatively defines a third passage that communicates the pressurized fuel chamber to the second chamber. Furthermore, the fuel delivery circuit also basically includes a fuel jet, disposed along the first passage, and a check valve, disposed along the first passage between the fuel jet and the first chamber. In this way, the first passage, the first chamber, the second passage, the second chamber, and the third passage cooperatively define an elongated fuel passage between the pressurized fuel chamber and the fuel supply nozzle for delivering fuel into the valve chamber.
According to the present invention, the elongated fuel passage defined in the fuel delivery circuit generally serves to increase the fluid resistance of the fuel delivery circuit as compared to other conventional fuel delivery circuits. During low-speed operation of the engine (such as during idling), since both the speed and level of fuel flow in the fuel delivery circuit are characteristically low, the fluid resistance through the fuel delivery circuit is therefore low as well. As a result, the increased fluid resistance attributable to the elongated fuel passage of the fuel delivery circuit is practically negligible during low-speed operation of the engine. Thus, in utilizing the fuel delivery circuit according to the present invention, a necessary amount of fuel is still successfully delivered to the engine during low-speed operation. On the other hand, during acceleration and/or high-speed operation of the engine, the amount of fuel delivered to the engine is sufficiently restricted by the elongated fuel passage such that the amount of fuel delivered to the engine increases in nearly linear proportion to the number of revolutions per minute of the engine. As a result, the delivery of an excessive amount of fuel to the engine during acceleration and/or high-speed operation of the engine is successfully avoided. Thus, in utilizing the fuel delivery circuit according to the present invention, a fuel supply characteristic which is better matched to the amount of fuel that the engine actually requires is successfully obtained.
In a preferred embodiment of the present invention, the fuel delivery circuit also includes a fuel pump and an inlet valve. The inlet valve is preferably situated between the fuel pump and the pressurized fuel chamber such that the inlet valve is able to provide fluid communication between the fuel pump and the pressurized fuel chamber. In addition, the inlet valve is also preferably situated proximate to the opening defined by the third passage in the enclosure of the pressurized fuel chamber. The pressurized fuel chamber, on the other hand, preferably has a substantially constant pressure and maintains a substantially constant level of fuel. In this way, a continuous supply of fuel, including fresh fuel unaffected by surrounding heat, is introduced into the third passage. As a result, smooth operation of the engine is ensured.
Also in a preferred embodiment of the present invention, the first chamber of the fuel delivery circuit is preferably situated under the fixed end of the fuel supply nozzle such that the first chamber structurally accommodates the check valve. In addition, the first chamber is also preferably situated such that the floor of the second chamber is higher than the floor of the first chamber. The elongated fuel passage, on the other hand, is preferably both substantially non-vertical and substantially non-linear. Furthermore, the elongated fuel passage, from the pressurized fuel chamber up to the fuel jet, preferably has a diameter which is larger than the inner diameter of the fuel jet.
In a highly preferred embodiment of the present invention, a fuel delivery circuit as described above is specifically incorporated in a rotary throttle valve type carburetor and accelerator system. Such a system includes a carburetor body, having a cylindrical valve chamber defined therein which crosses an intake passage defined therethrough, and a cylindrical rotary throttle valve, having a throttle bore. The cylindrical rotary throttle valve is fitted in the cylindrical valve chamber such that the throttle valve moves rotatively and slidably within the carburetor body. In addition, the system also includes a fuel supply nozzle, fixed at the bottom of the cylindrical valve chamber and protruding into the valve chamber to the throttle bore of the throttle valve, and a needle, supported by the throttle valve for insertion into the fuel supply nozzle. Furthermore, the system also includes an intermediate wall, connected to the bottom of the carburetor body, having a first chamber and a second chamber separately defined therein. An enclosure, having a pressurized fuel chamber, is disposed under the intermediate wall. A check valve and a fuel jet, also included within the system, are disposed in a first passage that communicates the first chamber to the fuel supply nozzle. A second passage included within the system communicates the second chamber to the first chamber, and a third passage within the system communicates the pressurized fuel chamber to the second chamber. In this way, the first passage, the first chamber, the second passage, the second chamber, and the third passage within the system all cooperatively define an elongated fuel passage between the pressurized fuel chamber and the fuel supply nozzle for delivering fuel into the valve chamber.
Objects, features, and advantages of the present invention include providing a fuel delivery circuit having an elongated fuel passage, wherein the elongated fuel passage sufficiently restricts the amount of fuel delivered to an engine during acceleration and/or high-speed operation, and also providing a fuel delivery circuit which is compact, rugged, durable, of relatively simple design, of economical manufacture and assembly, and which has a long, useful life in service.